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THERMO Spoken Here! ~ J. Pohl © ~ 2018 | www.ThermoSpokenHere.com (B1400-081) |

The glass U-shaped tube contains 11 centimeters of "Fluid A" (in the left leg) above water.
**Calculate** the density of fluid **A**.

**♦ **Since the fluids are static, the hydrostatic equation applies. As a first task in applying the hydrostatic equation, one searches for physical scenario to find a place where the pressure is known. Sometimes there is no place where the pressure is known explicitly. In those cases there is usually a place where the pressure can be reasonably assumed. In this problem, the place is the the water surface on the right side; there the pressure is assumed atmospheric. We write the hydrostatic path from there downward through the bend then upward through both fluids to arrive at the surface of **Fluid A** (in the left leg).

**p**_{atm} + **ρ**_{water}g_{o}
**(0.08m) - ρ**_{A}g_{o}(0.13 m) = **p**_{atm}.

The "principle" was applied above. So go ahead and do algebra to it!

**ρ**_{A} = (8/13)**ρ**_{water}
= (8/13) 62.4 lbm/ft³

Therefore we determine the density to be: **ρ**_{A} = 38.4 lbm/ft³.